Hi are you still planning to do this trip?. I think your route is well thought out as it would be easier to go to Myanmar from KL on air Asia and then use the same airline to fly to Bangkok. Air Asia is a good budget airline with terrific service. You can then fly in to Sieam Reap or go to Saigon and do a speed boat trip to Sieam Reap via ton-ley sap waterways.
I am interested in the Myanmar and if time permitting Vietnam leg of the tour as I have been to other places on my previous travels, but have to keep all this within a 10 day time frame as I do not have a lot vacation days left. Let me know if you are still planning on doing this trip